Method of manufacturing annular laminated cores for transducers



Dec. 6, 1966 L. w. CAMP METHOD OF MANUFACTURING ANNULAR LAMINATED CORES FOR TRANSDUCERS Filed Jan. 21, 1964 INVEN TOR. LEON W. CAMP riz ATTORNEY United States Patent 3,289,279 METHOD OF MANUFACTURING ANNULAR LAMI- NATED CORES FOR TRANSDUCERS Leon W. Camp, Santa Monica, Calif., assignor to The Bend ur Corporation, North Hollywood, Calitl, a corporation of Delaware Filed Ian. 21, 1964, Ser. No. 339,163 Claims. (Cl. 29155.57)

This invention relates to transducers and more particularly to a method of manufacturing annular laminated cores for transducers of the magnetostrictive type.

The transducers with which this invention is concerned typically include one or more annular core members which are formed by loosely winding a thin strip of highly permeable magnetic material such as cobalt nickel on a mandrel until a desired thickness is obtained, annealing the strip to remove residual stresses and to cause itto retain the scroll configuration, bonding the layers together, and then wrapping a winding of insulated wire around the core in such manner as to permit radial vibration of the core in response to the change in direction of an alternating current applied to the winding. The most useful criterion of the quality of a magnetostrictive transducer is its electromechanical coupling coeflicient, a factor which is improved by increasing the magnetic permeability. It has been found that the magnetic permeability of such transducers is seriously degraded by residual strains in the magnetic material employed. It is, therefore, an object of the present invention to provide a process for the manufacture of annular laminated cores for magnetostrictive transducers in which residual mechanical stresses are reduced to a minimum.

It is another object of the present invention to provide a method for the manufacture of annular laminated cores for magnetostrictive transducers which will assure uniform high quality in the cores.

It is another object of the present invention to provide a process for the manufacture of annular laminated cores for magnetostrictive transducers which will produce cores of greatly improved efficiency, thereby making it possible to reduce the size of the overall transducer as compared with those of comparable output which are presently available.

Other objects and advantages will become apparent from the following specification and the drawing, in which:

FIGURE 1 is a plan view of a core loosely wound on a mandrel;

FIGURE 2 is a plan view of the wound core and mandrel of FIGURE 1 placed in a container for receiving the binder and with excitation windings included;

FIGURE 3 is a plan view of a wound core and mandrel similar to that of FIGURE 1, but wherein the exciting winding is wrapped around the mandrel and core before the assembly is placed in the binder.

Referring now to FIGURE 1, a strip of fiat ferrous metal 10, which is preferably of high permeability such as cobalt nickel, is somewhat loosely wound on an annular mandrel 12 to form a scroll. The assembly is then exposed to considerable heat until the metal is annealed to a fully soft state. After the annealing process, the metal retains its wound configuration without need for significant restraining force. The scroll of FIGURE 1 is then placed on a new mandrel 13 and the assembly inserted into an annular tank 14 which contains a suitable binding agent, such as epoxy resin, for binding the layers of the scroll together to form a solid core. The scrolls may be very large and heavy, and such an annular tank may require a supporting structure such as the cross-members 16 to avoid deformation of the tank. In this arrangement the outside end of the scroll may be fastened to a 3,289,279 Patented Dec. 6, '1 966 point on the tank 14 as by a bolt 18. To avoid bonding the scroll to the mandrel 13, the inside layer of the scroll is usually separated from the mandrel by a strip of polytetrafluoroethylene material. The inside end of the scroll strip may be fastened by any suitable means to the mandrel or to the polytetrafluoroethylene strip. An exciting winding 20 is then wound around the entire assembly of mandrel, scroll and tank. When the winding 20 is energized by means of an alternating current of approximately half the resonant frequency of the scroll, the mandrel 13 is rotated to tighten the wound layers of the metal strip. During excitation the scroll pulsates radially, causing a substantial reduction in the friction between the layers, and much less force is required to pull the turns tight than is the case when the scroll is not excited. The excess binder may then be drained from the tank. The residual strain on the scroll is further reduced by continuing the excitation for a short time after the tension on the metal strip has been removed. The windings 20 are then removed, and the scroll is removed from the tank 14, after which it is exposed to the proper temperature environment to cure the binder. This leaves the scroll secured in position by very evenly distributed bonding material between the laminations, while the core metal itself is almost entirely free of residual stress.

While the arrangement of FIGURES 1 and 2 is excellent for making transducers of comparatively large size (of the order of from 2 feet to several feet in diameter), scrolls of much smaller size (such as 6-l2 inches in diameter) are more easily handled as shown in FIGURE 3. In this arrangement the mandrel 30 has loosely wrapped on its periphery a scroll 32 which has been annealed as described above, and the winding 34 is then wrapped around the mandrel and scroll. This assembly, or several such assemblies, may then be dipped into a tank containing the bonding material. This scroll 32 is also separated from the mandrel 30 by means of a layer of polytetrafluoroethylene material to avoid adherence of the scroll to the mandrel. An alternating current voltage of a frequency which is preferably about half the resonant frequency of the scroll is then connected to the terminals 36 and 38 of the winding 34. During this time a force is applied to the outside end 40 of the scroll strip which tends to tighten the scroll. After the scroll has been pulled up as desired, it is removed from the tank, the exciting winding 34 is removed, the excess bonding material is removed, and the scroll is cured as described above. When the bonding material is dry, the mandrel is remove-d, and the scroll is now ready to receive the regular operating windings.

While only a limited number of embodiments have been shown and described herein, it is recognized that modifications may be made within the scope of the present invention which is to be limited only by the scope of the following claims.

I claim:

1. In a method of manufacturing annular laminated cores for magnetostrictive transducers wherein is included the stage of loosely winding a length of thin ferrous metal strip on a circular mandrel until the layers are built up to form a scroll of approximately the desired radial thickness,

annealing said scroll to remove substantially all residual stress in said metal strip while causing said scroll to retain its form as wound,

placing the annealed scroll on a second mandrel, over a strip of binder-repellant material,

immersing said scroll and second mandrel in a tank containing a binder of epoxy resin,

the improvement comprising subjecting the immersed said scroll to an exciting field of alternating polarity 3 of a frequency which causes mechanical resonance of said scroll,

and applying tension to the ends of said strip during said excitation to tighten said scroll whereby said scroll is tightened as desired while retaining a minimum of residual mechanical stress.

2. A method of manufacturing annular laminated cores as set forth in claim 1 wherein said wound scroll and said second mandrel are placed in an annular tank containing said binder, and a plurality of turns of wire are wound around said tank, scroll and mandrel which are energized to create said exciting field.

3. A method of manufacturing annular laminated cores as set forth in claim 1 wherein a plurality of turns of wire are wound around said mandrel and said scroll; and said wire, mandrel and scroll are placed in said tank of binder during energization of said wire.

4. A method of manufacturing annular laminated cores for magnetostrictive transducers comprising the steps of loosely Winding a length of thin ferrous metal strip on a circular mandrel until the layers are built up to form a scroll of the desired thickness,

annealing said scroll to remove substantially all residual stress in said metal strip while causing said scroll to retain its form as wound,

placing the annealed scroll on a second mandrel, over a strip of binder-repellant material, immersing said scroll and said mandrel in a binder, creating an exciting field of alternating polarity of a frequency which causes mechanical resonance of the scroll,

drawing the layers of the loose scroll tight by applying tension between the ends of said strip during said excitation, thereby squeezing excess binder from be tween the layers of said scroll,

removing said scroll from said binder and exposing said scroll to the environmental conditions required to cure said binder.

5. A method of manufacturing annular laminated cores for magnetostrictive transducers comprising the steps of loosely winding a length of thin ferrous metal strip on a circular mandrel until the layers are built up to form a scroll of approximately the desired radial thickness,

annealing said scroll to remove substantially all residual stress in said metal strip while causing said scroll to retain its form as wound,

placing the annealed scroll on a second mandrel, over a strip of binder-repellant material,

immersing said scroll and second mandrel in a tank containing a binder of epoxy resin,

winding a substantial number of turns of wire around said scroll to form an annular coil and exciting said coil with an alternating current of a frequency which causes mechanical resonance of the scroll,

drawing the layers of the loose scroll tight by applying tension between the ends of said strip during said excitation, thereby squeezing excess binder from between the layers of said scroll,

removing said scroll from said binder and subjecting said scroll to the heat required to cure said binder.

No references cited.

CHARLIE T. MOON, Primary Examiner. R. W. CHURCH, Assistant Examiner. 

1. IN A METHOD OF MANUFACTURING ANNULAR LAMINATED CORES FOR MAGNETOSTRICTIVE TRANSDUCERS WHEREIN IS INCLUDED THE STAGE OF LOOSELY WINDING A LENGTH OF THIN FERROUS METAL STRIP ON A CIRCULAR MANDREL UNTIL THE LAYERS ARE BUILT UP TO FORM A SCROLL OF APPROXIMATELY THE DESIRED RADIAL THICKNESS, ANNEALING SAID SCROLL TO REMOVE SUBSTANTIALLY ALL RESIDUAL STRESS IN SAID METAL STRIP WHILE CAUSING SAID SCROLL TO RETAIN ITS FORM AS WOUND, PLACING THE ANNEALED SCROLL ON A SECOND MANDREL, OVER A STRIP OF BINDER-REPELLANT MATERIAL, IMMERSING SAID SCROLL AND SECOND MANDREL IN A TANK CONTAINING A BINDER OF EXPOXY RESIN, THE IMPROVEMENT COMPRISING SUBJECTING THE IMMERSED SAID SCROLL TO AN EXCITING FIELD OF ALTERNATING POLARITY OF A FREQUENCY WHICH CAUSES MECHANICAL RESONANCE OF SAID SCROLL, AND APPLYING TENSION TO THE ENDS OF SAID STRIP DURING SAID EXCITATION TO TIGHTEN SAID SCROLL WHEREBY SAID SCROLL IS TIGHTENED AS DESIRED WHILE RETAINING A MINIMUM OF RESIDUAL MECHANICAL STRESS. 